This invention relates to mechanical end face seal assemblies. More particularly, it relates to a high temperature mechanical end face seal assembly with a thermally stable mating ring.
Pumps, especially those in refineries and chemical plants, often handle difficult-to-seal liquids, including propane, butane, and other unstable, combustible, or toxic liquids. These liquids can cause short seal life and undesirable product leakage.
Mechanical end face seal assemblies are known and represent a successful solution to product leakage. Mechanical end face seal assemblies find wide applications in sealing liquids in pumps having a housing and an extending rotating shaft. The seal assemblies usually include a pair of annular seal rings that define a pair of relatively rotatable annular seal faces urged together to define a sealing interface. These seal rings are supported on the shaft and housing by assembly components. One seal ring, the primary ring, is axially movable and is urged by a compression spring or a metal bellows into face-to-face contact with the other seal ring, the mating ring, which is fixed against axial or rotational movement relative to the housing.
The seal assembly can include a single seal, tandem seal, or a double seal where a buffer fluid pressure is supplied at a pressure higher than the process fluid to be sealed in order to prevent leakage of the process fluid across the seal ring faces. Such mechanical seals are available from John Crane Inc., Morton Grove, Ill., and are disclosed in U.S. Pat. Nos. 5,901,965 and 5,954,341, the disclosures of which are incorporated herein by reference. The present invention represents a refinement in the mechanical seals of the type in U.S. Pat. Nos. 5,901,965 and 5,954,341.
FIG. 1 illustrates a traditional (prior art) stationary high temperature mechanical seal assembly 1010 for sealing between a housing 1020 and a rotating shaft 1016. The mechanical seal assembly 1010 of FIG. 1 has a single seal configuration, although other seal configurations, such as dual, tandem or triple seal configurations are also well known in the art.
The mechanical seal assembly 1010 includes a gland plate 1022 attached to the housing 1020. The mechanical seal assembly 1010 further includes a primary ring 1034 rotationally movable with the rotating shaft 1016 and a mating ring 1044 fixed against rotational movement.
The primary ring 1034 and the mating ring 1044 define radially extending seal faces 1040 and 1058 in engaging relationship with each other. The primary ring 1034 is interference fitted in a shell 1036. A bellows 1038 urges the shell 1036 and primary ring 1034 toward the mating ring 1044.
The mating ring 1044 includes a radially outward extending disk portion 1046. The disk portion 1046 of the mating ring 1044 is positioned within an annular groove 1072 defined on the gland plate 1022.
A spiral wound secondary seal 1048, formed of stainless steel and flexible graphite, is also situated in the annular groove 1072 defined on the gland plate 1022. In the installed position, the spiral wound secondary seal 1048 is located between the disk portion 1046 of the mating ring 1044 and the housing 1020.
A series of axially extending fasteners 1028 secure the gland plate 1022 to the housing 1020. The secondary seal 1048 and the disk portion 1046 of the mating ring 1044 are positioned axially between the gland plate 1022 the housing 1020. Tightening the fasteners 1028 clamps the secondary seal 1048 and the disk portion 1046 of the mating ring 1044 axially to secure the mating ring 1044 axially and radially. While this arrangement is effective in securing the mating ring 1044 to the gland plate 1022 and housing 1020, the application of a clamping force on the disk portion 1046 of the mating ring 1044 may distort the seal face 1058 of the mating ring 1044.
FIG. 2 illustrates another traditional (prior art) stationary high mechanical seal assembly 1110 for sealing between a housing 1120 and a rotating shaft 1116. The mechanical seal assembly 1110 includes a gland plate 1122 attached to the housing 1120. The mechanical seal assembly 1110 further includes a primary ring 1134 rotationally movable with the rotating shaft 1116 and a mating ring 1144 fixed against rotational movement.
The primary ring 1134 and the mating ring 1144 define radially extending seal faces 1140 and 1158 in engaging relationship with each other.
The mating ring 1144 includes a radially outward extending disk portion 1146. The disk portion 1146 of the mating ring 1144 is positioned within an annular groove 1172 defined on the gland plate 1122.
Two spiral wound secondary seals 1148 and 1149 are also situated in the annular groove 1172 defined on the gland plate 1122. In the installed position, one spiral wound secondary seal 1148 is located between the disk portion 1146 of the mating ring 1144 and the housing 1120. The other spiral wound secondary seal 1149 is located between the disk portion 1146 of the mating ring 1144 and the gland plate 1122.
Axially extending fasteners 1128 secure the gland plate 1122 to the housing 1120. The two secondary seals 1148 and 1149 and the disk portion 1146 of the mating ring 1144 are positioned axially between the gland plate 1122 and the housing 1120 tightening the fasteners 1128 clamps the secondary seals 1148 and the disk portion 1146 of the mating ring 1144 axially to secure the mating ring 1144 axially and radially. Similar to the mechanical seal assembly 1010 of FIG. 1, the application of a clamping force on the disk portion 1146 of the mating ring 1144 may distort the seal face 1158 of the mating ring 1144.
FIG. 3 illustrates a traditional (prior art) stationary high mechanical seal assembly 1210, having two seals in a tandem seal configuration, for sealing between a housing 1220 and a rotating shaft 1216. The mechanical seal assembly 1210 comprises an inboard seal 1212, closet to the housing 1220, and an outboard seal 1214 which operate together to seal the shaft 1216 relative to the housing 1220. The mechanical seal assembly 1210 further includes an inboard gland plate 1222, an outboard gland plate 1224 and a gland liner 1226.
The inboard seal 1212 includes a primary ring 1234 rotationally movable with the rotating shaft 1216 and a mating ring 1244 fixed against rotational movement. The primary ring 1234 and the mating ring 1244 define radial extending seal faces 1240 and 1258 in engaging relationship with each other. The mating ring 1244 includes a radially outward extending disk portion 1246. The disk portion 1246 of the mating ring 1244 is positioned within an annular groove 1272 defined on the inboard gland plate 1222 and an annular groove 1227 defined in the gland liner 1226.
Two spiral wound secondary seals 1248 and 1249 are also situated in the annular grooves 1272 and 1227 defined on the inboard gland plate 1222 and gland liner 1226. In the installed positioned, one spiral wound secondary seal 1248 is located between the disk portion 1246 of the mating ring and the inboard gland plate 1222. The other spiral wound secondary seal 1249 is located between the disk portion 1246 of the mating ring 1244 and the gland liner 1226.
A series of axially extending fasteners 1228 secure the two gland plates 1222 and 1224 together. The two secondary seals 1248 and 1249 and the disk portion 1246 of the mating ring 1244 are positioned axially between the inboard gland plate 1222 and the gland liner 1226. Tightening the fastener 1228 clamps the secondary seals 1248 and 1249 and the disk portion 1246 of the mating ring 1244 axially to secure the mating ring 1244 axially and radially. Similar to the mechanical seal assemblies 1010 and 1110 of FIGS. 1 and 2, the application of a clamping force on the disk portion 1246 of the mating ring 1244 may distort the seal face 1258 of the mating ring 1244.
The problem of transmission of distortion through the gland plate to the mating ring face is well known. The American Petroleum Institute (API) prohibits the use of clamped mating rings in their Standard 682, Second Edition (re: pg 36, para 6.1.4.1 and FIG. 21). The present invention eliminates this problem.
Another problem experienced in mechanical seal assemblies is associated with system pressure reversal. If secondary seals are not properly sized radially, a system pressure reversal will cause the secondary seal to leak. It is important to configure the secondary seal to maintain the sealing relationship. Furthermore, the API requires that Arrangement 3 seals, pressurized dual seal applications, be designed to stay closed during reverse pressure operation (pg 49, para 7.3.1.2).